629A GOLF II

In March 1958 the development of a new missile launch system D-4 with R-21 missiles was approved. It was planned to replace the D-2 launch system and allowed underwater missile firings. The R-21 missiles could be fired from a depth of 40-50 m at a speed of up to 4 knots at intervals of 5 minutes. The time for prelaunch preparation was approximately 45 minutes. After the launch system reached its IOC in May 1963 the re-equipment of the 629 submarines began. The submarines equipped with the new D-4 launching system were designated as 629A (Golf II). In early 1967 the upgrading of the first submarines under the project 629A was completed. In total 8 submarines from the Northern and Pacific fleet were outfitted with the D-4 launch system.

The improved twenty third submarine of the Golf class (629A) incorporated two improved R-21 missiles.